The invention concerns a sliding bearing material made from an aluminum alloy with 10 to 25 mass % tin.
A sliding bearing material of this kind is disclosed e.g. in DE 40 04 703 A1. The single embodiment describes an aluminum alloy with a composition of AlSn10NiMn1Cu0.5, wherein instead of tin, lead can also be added. With aluminum alloys of this kind which are used as sliding bearing material, a "soft phase" in the form of a tin or lead precipitate is required for ensuring good emergency running properties of a bearing produced from the sliding bearing material. Hard contaminating particles or abrasions are accommodated or embedded in this soft phase. The soft phase can also adapt to geometric conditions. The soft phase of tin, which does not dissolve in aluminum, is accepted in the form of block-like precipitates within the aluminum matrix.
Copper can be added to increase the strength of the aluminum matrix. Copper, in connection with aluminum, forms intermetallic phases, so-called hard material phases, such as Al.sub.2 Cu and finely distributed precursor stages thereof which increase the stability of the aluminum matrix when present as finely distributed precipitates (.ltoreq.1 .mu.m). This increases the stability under load and fatigue resistance of a sliding bearing material produced from the alloy. The aluminum alloy AlSn15Cu2 has been disclosed by the assignee under the trade name KS 985.3. This alloy has excellent tribological properties, but requires improvements for applications under extreme loads, such as e.g. connecting rod bearings in modern internal combustion engines.
Such improvements were attempted with the aluminum alloy disclosed in DE 40 04 703 A1 by adding manganese and nickel, in an attempt, according to this document, to increase the portion of hard substance phases, in particular, in the region of tin precipitates to improve binding of the tin precipitates in the aluminum matrix via the affinity of tin for nickel and manganese.
A certain proportion of hard substance phases or precipitates is believed to have positive effects on wear resistance in that the hard substance phases at the surface effect fine grinding of the sliding partner, e.g. the crank shaft, to ensure that roughness peaks of the steel sliding partner can be abraded. The hard substance phases also increase the stability under load of the bearing material.
Increasing the portion of intermetallic hard substance phases causes problems with respect to fatigue resistance and manufacturing. Cracks are formed during shaping, in particular during cold plating of the aluminum alloy on steel, requiring a pass producing approximately 50% shaping.
U.S. Pat. No. 4,471,029 describes an aluminum silicon tin sliding bearing material with 0.5 to 5, preferably 2 to 5 mass % silicon with the addition of at least one of the following elements: lead, indium, thallium, cadmium, bismuth, copper, magnesium, chrome or manganese. The document teaches formation of elementary silicon precipitates having a particular dimensional spectrum.
It is the underlying purpose of the present invention to improve an alloy of the above mentioned kind such that it has better stability under load than the conventional aluminum tin copper or aluminum tin copper nickel alloy and better deformability, in particular plateability.